The present invention relates to a resin composition useful in the formulation of die attach adhesives, encapsulants, underfills, via fills, prepreg binders, polymer solder masks and polymer bumps on flip chip or BGA assemblies.
As uses for semiconductor devices continue to increase, there is a growing demand for adhesive compositions and resin formulations useful in the packaging of such devices both on the board and substrate level. Adhesives are used, for example, to attach dies to semiconductor packages under a variety of conditions. Underfills are used to reduce stress and increase the reliability of solder ball joints found between the substrate, i.e., package, and the die. Encapsulants are used to completely encapsulate, seal and bond a die to a semiconductor package. Via fills are used in both board and laminate substrates to fill the vias in the substrate. Binders found in the manufacture of printed circuit boards and laminate substrates are needed as part of the structural composite of the laminate, serving to bind various metal layers and circuitry together into a single functioning unit. The alternating layers of circuitry, metal planes and vias, along with a matte material, such as glass fibers (which help with structural integrity), are bound together with the organic polymer binder to create the total laminate. Simple layered structures of glass and binder are often sold in a pre-cured state call “prepregs”, which are later head-bonded or laminated together as part of the process that creates the laminate substrate or printed circuit board.
To be useful in the manufacture of semiconductor devices, die attach adhesives and the like must meet certain performance, reliability and manufacturability requirements as dictated by the particular application. Performance properties for which there are typically minimum requirements include adhesion, coefficient of thermal expansion, flexibility, temperature stability, moisture resistance and the like. Reliability requirements are typically evaluated by the device's sensitivity to moisture-induced stress. Manufacturability requirements generally include specific requirements for rheology, cure rates and usable pot life and the like. For both the via fill and laminate structures, properties must be met that exhibit superior dimensional stability to processes such as plating, machining, sanding and baking.
Moisture resistant and flexible materials are highly desirable for the manufacture of semiconductor devices. Moisture inside a package turns to steam and expands rapidly when the package is exposed to high temperatures (for instance during solder reflow, infrared or convection baking, or if the package is contacted by molten solder). Under certain conditions, moisture induced pressure will initialize package failure such as internal delamination in the interfaces, internal cracking, wire necking, bond damage, and of course the obvious external crack i.e. popcorning.
Resin compositions comprising a cyanate ester and epoxy resins have been demonstrated to be useful as die attach adhesives, underfills, and the like. While the performance characteristics for such resin compositions are adequate for some applications, there is a continuing need to improve reliability and manufacturing performance of the compositions. Currently available compositions address some, but not all, of the following performance criteria: long pot life, fast cure, and high adhesion. Currently available materials tend to exhibit high rigidity with a Young's modulus of 4-7 GPa at room temperature and low moisture resistance. A need therefore exists for compositions that exhibit adequate flexibility while providing sufficient moisture resistance.